The present invention relates to a buoyancy force sensor for a hydrometer to measure the density of a liquid mixture. More particularly, the present invention relates to such a sensor mounted within an outlet of a storage tank used in storing the liquid mixture. In another aspect, the present invention relates to such a sensor employed in an interlock for the storage tank to prevent dispensing of a respirable liquid cryogen when the liquid contains unsafe levels of oxygen.
The use of hydrometers for determining the density of a mixture is well known in the art. In known hydrometers, a float is provided that exerts a buoyancy force that is dependent upon the density of a mixture. Commonly, the height of the float is observed within a column of a liquid sample to determine the density. In mixtures that by and large contain two components, each of different density, the density measurement will define the component concentration of the mixture. Component concentration of a mixture is important to quantify in order to properly conduct a variety of commercial processes. If density is used for such quantification, the measurement becomes difficult because density can vary within any bulk of mixture to be utilized.
As can be appreciated, where the mixture will come into human contact, component concentration can become especially critical. For instance, cryogenic oxygen and nitrogen mixtures, or liquid air for that matter, are used in a variety of cryogenic processes to ensure that such processes are conducted in a safe, respirable environment. At one extreme, if not enough oxygen is present, the evolved vapors will act as a suffocant. If too much oxygen is present, the resultant atmosphere will be produce highly flammable conditions in the environment. It is a relatively simple matter to ensure that the oxygen concentration is sufficient to support life at the time a container is filled with the respirable mixture. However, since nitrogen is more volatile than oxygen, heat leakage into the container will cause oxygen enrichment of the liquid due to a preferential boil off of nitrogen. Therefore, over time, it becomes difficult to ensure that the liquid being dispensed has not become so enriched in oxygen as to present a fire hazard
As will be discussed, the present invention provides a sensor to sense buoyancy force that ensures density will be measured in the liquid as dispensed. Such sensor is particularly useful for service as a sensor for an interlock to prevent the dispensing of a respirable liquid cryogenic mixture if such liquid has an unsafe oxygen level.